The present invention relates to a substrate cleaning method and a substrate cleaner.
Of the substrate cleaning methods for use in a semiconductor fabrication process, those utilizing physical force are divided into two types: contact and non-contact. As the contact type method, one in which an object to be cleaned is scrubbed with a pencil sponge or roll sponge made of PVA is known. As the non-contact type method, one which utilizes sound pressure (ultrasonic vibrations) or hydraulic pressure is known.
The chemicals used in these types of physical cleaning include, for example, ones containing anionic ammonia water, ones having oxidative capability (ozonized water, hydrogen peroxide water), and cationic ones such as hydrochloric acid and hydrofluoric acid.
When supplying the mixture of those chemicals to a wafer (semiconductor substrate), it is necessary to mix plural kinds of chemicals (for example, ozonized water and ammonia water) outside the cleaner itself beforehand. In other words, equipment other than the cleaner itself is needed. Although various methods have been reported in which chemicals are mixed immediately before the portion of the wafer to be processed, all of them are basically methods of mixing chemicals.
In the above described methods of mixing chemicals beforehand, when using a chemical containing a highly self-reactive substance (for example, when using ozonized water), ozone molecules in the ozonized water undergo self-decomposition and the ozone concentration decreases while the ozonized water is being supplied to the portion of the wafer to be processed. Furthermore, depending on the chemicals to be mixed with the ozonized water (for example, alkaline solutions such as ammonia water), the ozone concentration may extremely decrease. Thus, the physical cleaning methods in current use have a problem that, when using a chemical mixture containing a highly self-reactive substance, a wafer cannot be cleaned effectively.
In the case of contact type cleaning methods, it is difficult to remove particles (contaminants) in a recess of an object to be cleaned which are impossible to bring in contact with a cleaning chemical. Such a recess includes, for example, those formed dishing due to chemical mechanical polishing (CMP), a scratch, or an alignment marker, as shown in FIG. 9. Such particles include, for example, abrasive grains in a slurry used in CMP.
In order to remove particles adsorbed onto a recess, it is necessary to use non-contact type methods which utilize sound pressure or hydraulic pressure. However, in the cleaning methods utilizing sound pressure, in particular, ultrasonic vibrations, there is a difference in cleaning effect depending on the concentration of the gas dissolved in the chemical used.
Accordingly, in order to make ultrasonic cleaning effective, ultrapure water is needed which has undergone dissolved gas control, and which in turn requires facilities such as a dissolving system. This requirement gives rise to a problem of imposing higher costs on the factory side.
The above described contact type cleaning methods, which utilize a pencil sponge, etc., are effective in removing particles adsorbed on a wafer. On the other hand, the non-contact type cleaning methods are effective in removing particles in a recess, which cannot be removed by the contact type cleaning methods.
Accordingly, when there exists a recess on a wafer, in order to fully remove the particles remaining on the wafer, it is necessary to carry out contact type and non-contact type physical cleaning at the same time, which requires two cleaning modules to be prepared. This leads to an increase in cleaning cost.
As described above, the conventional substrate cleaning methods utilizing physical force have a problem in that, when using a chemical mixture containing a highly self-reactive substance, effective cleaning of a wafer is impossible.
Further, when there exists a recess on a wafer, in order to fully remove the particles remaining in the recess, it is necessary to carry out both contact type and non-contact type physical cleaning at the same time. However, this requires two cleaning modules to be prepared and, therefore, gives rise to a problem of increasing cleaning costs.
The present invention was made in view of the above problems. Accordingly, the object of the present invention is to provide a substrate cleaning method and substrate cleaner which provide effective cleaning even with a chemical containing a highly self-reactive substance, prevent cleaning costs from increasing, and provide effective cleaning of the object having a recess thereon.
Of aspects of the present invention disclosed in the present application, the typical one will be described below. In order to accomplish the above object, the substrate cleaning method of the present invention includes: a step of supplying a liquid and a gas onto an object to be cleaned and dissolving the above gas in the above, liquid so as to produce a gas-dissolving (i.e., gas-containing) liquid; and a step of cleaning the above object to be cleaned with the above gas-dissolving liquid. The object to be cleaned is, for example, a wafer (substrate) or a wafer (substrate) having been subjected to processing such as CMP.
If a gas-dissolving liquid is produced on an object to be cleaned as described above, even in cases where the gas-dissolving liquid contains a highly self-reactive substance, the gas-dissolving liquid can be supplied to the object to be cleaned immediately after its production. Therefore, the concentration of the highly self-reactive substance can be prevented from decreasing. Accordingly, even if a chemical containing a highly self-reactive substance is used, cleaning can be carried out effectively. This method is quite effective, particularly when the use point is a system open to atmosphere.
Furthermore, supplying the gas-dissolving liquid to the object to be cleaned at a high pressure enables non-contact type physical cleaning. Therefore, the object having a recess can be cleaned effectively. In addition, the steps of producing the gas-dissolving liquid and of supplying the gas dissolving liquid to the object to be cleaned at a high pressure can be carried out in one cleaner, so that cleaning costs are prevented from increasing.
Further, the substrate cleaner of the present invention includes: a mixing portion, which consists of a sponge-like member and has a through-path formed by removing a certain area of sponge-like member; a liquid introducing means for introducing a cleaning liquid into the above through-path; and a gas introducing means for introducing a cleaning gas into the above mixing portion.
It is to be understood that the expression xe2x80x9ca through-path formed by removing a certain area of the sponge like memberxe2x80x9d, which refers to the process of forming a through-pass, is used only to express the component (the mixing portion) of the present invention in a simple manner, and is not intended to limit the forming method of the above component.
In the construction as described above, if a cleaning liquid is introduced into the through-path by the liquid introducing means at, for example, a high pressure, the cleaning gas which has been introduced into the mixing portion by the gas introducing means can be introduced into the through-path on the aspirator""s principle. In other words, the cleaning gas and liquid can be easily mixed in the through-path, and thereby a gas-dissolving liquid can be easily produced. Thus, the cleaning method according to the present invention can be carried out.